There are two characteristics of hydrangeas that lead to all the confusion surrounding this perennially popular genus: whether they bloom on new or old wood, and their flower color. We’ve covered the former extensively on this page, so now, let’s talk plainly about which hydrangeas change color, how they do it, and which ones you can, and can’t, control. I’d like to go over each of the main types of hydrangeas you’ll find on our website and out at the garden center – bigleaf, mountain, panicle, smooth, oakleaf, and climbing hydrangeas.
Bigleaf and mountain: these hydrangeas change color based on soil chemistry
Bigleaf and mountain hydrangeas can shift from pink to purple or blue depending on the soil pH and the presence of aluminum. Aluminum is a naturally occurring element in many soils – in fact, it’s the third-most abundant element in the earth’s outer layer. However, aluminum is only available for the plant to metabolize in acidic soils. Therefore, in order to get blue flowers on a hydrangea, the soil must both contain aluminum and be acidic. If only one of those conditions is true, these same hydrangeas will bloom pink or red.
If you would like to change the color of your bigleaf or mountain hydrangea flowers, let’s talk about what to add to the soil to change the pH*.
Alkaline soil – pH of 7.5 and above
– pink flowers
If your soil is neutral or acidic you can add lime to raise the pH.
Neutral soil – pH of 6.5 to 7.5
– usually a bit of a blend of color, leaning toward pink
Acidic soil – pH of 6.5 and below
– blue or purple flowers
If your soil is alkaline or neutral, you can apply garden sulfur with aluminum added. It’s really the aluminum that the plant absorbs that changes the flowers blue, but the soil needs to be acidic enough for the process to happen. Read the labels of the products at your garden center carefully to make sure the one you choose includes aluminum.
* Changing the soil pH takes time, so be patient. Don’t apply more than the recommended amount of the product you buy as this can drastically affect the hydrangea and surrounding plants.
For example – if the pH is lowered too quickly, it can lead to some purple or brown tints in the foliage because the plant cannot take up phosphorous from the soil.
Panicle and oakleaf: these hydrangeas change color based on temperature and day length
The progression from white or green flowers in summer to vivid shades of pink, burgundy, and red in late summer/early fall is a hallmark of panicle hydrangeas; certain oakleaf hydrangeas, like Gatsby Pink, also develop dazzling color as they mature.
The color change on these hydrangeas is brought on by the shorter days and cooler temperatures that develop as summer gives way to fall. There is really nothing that the gardener can do to encourage better color with these plants aside from keeping them well-watered so they don’t dry out and turn brown.
One caveat here: not all panicle and oakleaf hydrangeas develop color. Many, like Puffer Fish panicle hydrangea, stay white up until the first frost, when they turn brown.
Smooth and climbing: these hydrangeas don't undergo dramatic color changes
Frequently Asked Questions
Why did my hydrangea flowers turn brown so early?
Hydrangea flowers will turn brown prematurely (instead of having a gentle color transition) when they get too warm at night, aren’t receiving enough water, or are frequently getting overhead water. There is no way to revive a flower, so if you don’t like the look of the browned bloom, the best course of action is to remove those flowers.
Should I deadhead my brown hydrangea flowers?
It’s all about your preference. Sometimes they’ll age to a pretty, albeit, muted color. Some folks really like to see them stick around throughout the winter to provide some interest. If you don’t enjoy the color or the blooms just aren’t attractive, you can deadhead them to tidy up the plant’s appearance. Just follow the stem of the spent flower back to the first set of leaves and make a clean cut.
Can coffee grounds change a hydrangea’s flower color?
No, they cannot. Coffee grounds add organic matter to the soil but they do not impact the aluminum content or pH, so have no effect on color.
What determines the color of hydrangeas?
Two things: whether that species of the hydrangea changes color at all, and its specific genetics. Not all hydrangeas are capable of achieving the same intensity or hue in color – that’s a genetic trait.
Can you change the color of any hydrangea?
No you cannot, only bigleaf and mountain hydrangeas will change color due to soil chemistry.
How long does it take to change a bigleaf or mountain hydrangea’s flower color?
It can take a year or longer. Generally, the proper conditions must exist when the plant is forming its flower buds, not when it’s already open.
Can I use a home-prepared solution to change the soil pH?
It’s best to just use a pre-prepared lime or sulfur product. They are 100% proven to work, as opposed to the many garden myths that do not work and/or produce spotty results (like nails, coffee grounds, pennies, banana peels, etc.).
Does pH affect the color of all types of hydrangea?
No, it only affects bigleaf and mountain hydrangeas. All other types will have the same color blooms no matter the soil pH.